Some computers in today's networks operate using one or more limit values. A limit value can define, for a particular packet, how long that packet is to be allowed to exist in the network. When the limit value has expired, for example because it has been successively decremented as the packet is forwarded, the packet can be discarded. This can seek to avoid the likelihood that a packet remains indefinitely in the network.
As a particular example, Internet Control Message Protocol (ICMP) requires an internet protocol (IP) router to drop an IP packet if its Time-To-Live (TTL) value is 0, and to send back an ICMP Time Exceeded error message to the sender of the packet. A so-called traceroute program (e.g., traceroute in UNIX/Linux, tracert in Windows) can be implemented and can use the ICMP feature to attempt to learn the path from source to destination.